Step 3: Condenser

The refrigerant entering the condenser is now a hot, high pressure refrigerant gas. The condenser is shown on the pressure-enthalpy diagram as a horizontal line. This horizontal line is a line of constant pressure, corresponding to the discharge pressure of the compressor. The condenser proceeds from right to left in the following three steps:

(1) The superheated gas cools down to saturation temperature [C' 160 °F to D' 140 °F]. Cooling takes place as heat flows from the hot refrigerant gas to the condenser cooling medium.

(2) Next, the 100% saturated vapor at D' is converted to 100% saturated liquid at D''. Heat is lost to the condenser cooling medium as the vapor is condensed to a liquid.

(3) Finally, the 100% saturated liquid is sub-cooled from D'' to D'''[140 °F to 115 °F]. In an ideal condenser, no sub-cooling occurs. Once the refrigerant is a fully saturated liquid, any additional heat loss results in a decrease in temperature. This cooling of the saturated liquid is referred to as sub-cooling. In this example, the refrigerant has gone through 25 °F of sub-cooling and resulted in a sub-cooled temperature of 115 °F.

Condenser Movement on the Pressure Enthalpy Diagram for the Mechanical PE Exam

A common question is to determine the heat expelled by the condenser, which is shown in the figure above as the difference between the condenser entering condition (H2) and the leaving condition (H4). The equation to determine the net condenser effect is shown below. This equation multiples the refrigeration flow rate by the change in enthalpy between the entrance and exit of the condenser.

Pressure Enthalpy Diagram for the Mechanical PE Exam with Constant Temperature Lines

The x-y axes of the P-H diagram are the pressure lines running from left to right. The enthalpy lines are the vertical lines. The skeletal graph shown below shows the pressure-enthalpy lines.

Net Condenser Work Equation